About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / networking / rmnet.txt




Custom Search

Based on kernel version 4.15. Page generated on 2018-01-29 10:00 EST.

1	1. Introduction
2	
3	rmnet driver is used for supporting the Multiplexing and aggregation
4	Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm
5	Technologies, Inc. modems.
6	
7	This driver can be used to register onto any physical network device in
8	IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator.
9	
10	Multiplexing allows for creation of logical netdevices (rmnet devices) to
11	handle multiple private data networks (PDN) like a default internet, tethering,
12	multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends
13	packets with MAP headers to rmnet. Based on the multiplexer id, rmnet
14	routes to the appropriate PDN after removing the MAP header.
15	
16	Aggregation is required to achieve high data rates. This involves hardware
17	sending aggregated bunch of MAP frames. rmnet driver will de-aggregate
18	these MAP frames and send them to appropriate PDN's.
19	
20	2. Packet format
21	
22	a. MAP packet (data / control)
23	
24	MAP header has the same endianness of the IP packet.
25	
26	Packet format -
27	
28	Bit             0             1           2-7      8 - 15           16 - 31
29	Function   Command / Data   Reserved     Pad   Multiplexer ID    Payload length
30	Bit            32 - x
31	Function     Raw  Bytes
32	
33	Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command
34	or data packet. Control packet is used for transport level flow control. Data
35	packets are standard IP packets.
36	
37	Reserved bits are usually zeroed out and to be ignored by receiver.
38	
39	Padding is number of bytes to be added for 4 byte alignment if required by
40	hardware.
41	
42	Multiplexer ID is to indicate the PDN on which data has to be sent.
43	
44	Payload length includes the padding length but does not include MAP header
45	length.
46	
47	b. MAP packet (command specific)
48	
49	Bit             0             1           2-7      8 - 15           16 - 31
50	Function   Command         Reserved     Pad   Multiplexer ID    Payload length
51	Bit          32 - 39        40 - 45    46 - 47       48 - 63
52	Function   Command name    Reserved   Command Type   Reserved
53	Bit          64 - 95
54	Function   Transaction ID
55	Bit          96 - 127
56	Function   Command data
57	
58	Command 1 indicates disabling flow while 2 is enabling flow
59	
60	Command types -
61	0 for MAP command request
62	1 is to acknowledge the receipt of a command
63	2 is for unsupported commands
64	3 is for error during processing of commands
65	
66	c. Aggregation
67	
68	Aggregation is multiple MAP packets (can be data or command) delivered to
69	rmnet in a single linear skb. rmnet will process the individual
70	packets and either ACK the MAP command or deliver the IP packet to the
71	network stack as needed
72	
73	MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding....
74	MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad...
75	
76	3. Userspace configuration
77	
78	rmnet userspace configuration is done through netlink library librmnetctl
79	and command line utility rmnetcli. Utility is hosted in codeaurora forum git.
80	The driver uses rtnl_link_ops for communication.
81	
82	https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/dataservices/tree/rmnetctl
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.